Scientists have new clues about the roots of an unusual condition called alien hand syndrome.
In alien hand syndrome, the patient's hand moves involuntarily, sometimes forcing the patient to "use their healthy hand to restrain the alien hand's actions," Swiss doctors report in today's early online edition of the Annals of Neurology.
Alien hand syndrome is "rare and distressing," write the doctors, who include Frederic Assal, MD, of the department of clinical neurosciences at University Hospital in Geneva, Switzerland.
Assal and colleagues studied a 70-year-old man who developed alien hand syndrome after suffering a stroke.
Alien hand syndrome affected the man's left hand. The stroke also affected his vision on the left side of his body, so he sometimes didn't know what his left hand was doing.
"For instance," write the doctors, "his left hand could grasp and manipulate parts of clothes or objects, even tear them into pieces, while the patient was [sitting] in his armchair and unaware of these involuntary movements."
Alien Hand Syndrome Brain Scan
Assal's team scanned the man's brain using functional magnetic resonance imaging (fMRI). The brain scans were done while the man's arms and forearms were strapped down, out of the man's sight, while he was resting or while he deliberately moved his right or left hand.
While the man deliberately moved his right or left hand, the brain scans showed activity in several brain areas.
But while the man rested, the fingers on his left hand flexed and relaxed slowly and repetitively. Those were involuntary movements, according to Assal's team.
During those alien hand movements, the brain scans only showed activity on the right side of the brain in an area called the motor cortex.
Voluntary movements involve the motor cortex, but they also engage other parts of the brain, the doctors note.
Assal and colleagues didn't study any other people with alien hand syndrome, so it's not clear if this particular patient represents all people with alien hand syndrome.
However, the doctors note that their findings may shed new light on the brain's control of voluntary and involuntary motions.
This article was reviewed by Brunilda Nazario, MD.
SOURCES: Assal, F. Annals of Neurology, July 17, 2007; online "Early View" edition. News release, John Wiley & Sons, Inc.